Modulated carrier wave system



Sept. 24, 1935. Wl T- DlTCl-AM' 2,015,175

l MODULATED CARRIER WAVE SYSTEM v Filed June 29, 1935 w d i Gers/w ATTORNEY Patented Sept. 24.,Y 1935 UNITED VAT NT @FFME Y 2,015,175 MoDULATEn carisma WAVE sYsTEM William Theodore Ditch assignor to vRadio C corporation of Delawar am, Chelmsford, England, poration of America, a e

5 Claims. (Cl. 179-171) This invention relates to radio and other modulated carrier wave systems and has for its object to provide an eiicient and simple method for modulating a high frequency carrier wave.

According to this invention energy from a high frequency carrier wave source is transferred to a loa-d circuit in a differential manner by means of two energy transferring circuits, each including a tuned circuit, and means are provided for simultaneously and oppositely varying the natural frequency of said tuned circuits in dependence upon the modulating potentials. The character of the energy supplied to the load circuit will be determined largely by thencharacter of the energy in that circuit which supplies the largest amount of energy to the load circuit at a particular instant. The load circuit may be constituted for example by an aerial circuit.

The invention is illustrated in the accompanying diagrammatic drawing, throughout which like reference characters indicate like parts, and in which Figures l to 3 inclusive show various modifications of the modulation circuits of the present invention.

Referring to Figure 1, which shows one Way of carrying out the invention, the output circuit of a high frequency thermionic valve oscillator V1 is inductively coupled totwo energy transferring circuits E1, E2, each consisting of a condenser C in series with inductance and each thus constituting a tuned circuit. The inductance or a portion L1 thereof of each tuned circuit is variably coupled to the output inductance coil L2 of the high frequency oscillator and the said two tuned circuits are also variably inductively coupled differentially at M1 and M2 to anaerial circuit, the

differential coupling being elf-ected by two coils L3, L1 in series between the aerial and earth. If these circuits E1 and E2 are in resonance with the exciting current from L2 and are equally coupled'thereto, as shown,'no carrier wave will appear in the aerial because of the differential coupling at M1, M2 to the opposedv inductances L3, L1. Two triodes V2, V3 are provided for modulating vpurposes and the modulating potentials are applied simultaneously and in phase opposition to the grids thereof, e. g., by means of a center-tapped transformer. The plate circuit of one triode contains a coil L5, which is inductively coupled to a part Le of the inductance of one tuned circuit, while the plate circuit of the other triode contains a corresponding coil L5, which is inductively coupled to the correspond- ,'ing'inductance portion Ls in the other tuned lcircuit. It will thus be seen that since the modulating potentials are applied to the grids of the modulating trio-des in phase opposition the effect of a given modulating potential will be to increase the inductance of one tuned circuit, say E1, and decrease that of the other, say E2. This 5 say E1, and decrease that of the other. This dephases the currents therein so that they no longer oppose in the aerial inductances La, L4 and consequently the amplitude of the carrier Wave in the aerial increases and decreases in 10 accordance with the signal potentials. Suitable polarizing potentials may be applied as indicated to the anodes and grids of the sai-d modulating triodes in order to adjust them to a suitable operating condition. l5 In a modification shown in Figure 2 the two tuned circuits E1, E2 of Figure l are in effect combined in a composite circuitconsisting of a pair of inductances L7, L7 shunted by condenser K1 in series with another pair of inductances 2 0 La, L3 shunted by a condenser K2, the series connected pair of condensers being in parallel with the series connected pairs of inductances as illustrated. The junction between the condensers K1, K2 is connected to the junction point be- 25 tween theadjacent inductances L1, L3 through a coupling coil L9, which is inductively coupled to a further coil L10 associated with the output inductances, or, as illustrated, forming part of the output circuit of the high frequency oscillator V1. 30 One of the inductances L7, and one of the inductances L3, are inductively coupled to two series connected coils L3, L1 in an aerial circuit as shown. These last mentioned inductive couplings are opposite in sense so that a differential 35 effect is obtained. As in the previous construction two modulating valvesv V2, V3 are provided and modulating potentials are applied to the grids thereof in phase opposition. The output circuit of valve V2 is inductively coupled by a 40 coil L5 to one of the inductances L3 in the composite circuit, While the output circuit of the other valve V3 is inductively coupled by a corresponding coil L5 to one of the inductances L7 in the composite circuit.

Figure 3 illustrates a slight modification of the last described arrangement, the junction point between the two series connected condensers K1, K2 in the composite circuit being directly connected without the interposition of the coil L9 of 50 Figure 2 to the junction point between the two series connected inductances L, and Ls. High frequency carrier oscillations from the drive or oscillator Valve V1 are applied to the composite circuit by inductive coupling between the output 55 inductance of said oscillator or a part L10 thereof and a further inductance Lg which is shunted across the two series condensers K1, K2.

Although in the actual embodiments described modulation is effected by oppositely varying the effective inductances in the tuned circuits, magnetic coupling being resorted to, it will be apparent that variation of the natural frequencies, of the two tuned circuits in opposite sense may equally well be effected by utilizing the modulating potentials to vary the capacities in these two circuits, or the inductance of one circuit and the capacity of the other can be varied simultaneously or both the inductance and the capacity in each circuit may be varied. The important feature is merely that the modulating potentials shall oppositely vary the relative phase of the currents in the two tuned circuits, so that these currents no longer oppose each other and there results a variation in the amplitude of the carrier wave energy fed to the aerial.

The source of high frequency carrier oscillations employed in carrying out this invention should be of such a nature as to be substantially constant in frequency and not easily varied by the effect of the modulating means employed. It is therefore preferred that the high frequency source whose output is transferred to the tuned circuits shall be not a high frequency generator but a high frequency amplifier valve driven by a high frequency generator and preferably the generator is maintained at substantially constant frequency by mechanically resonant means or piezo electric means or the like in manner well known per se.

Although the invention has been above described as incorporatingv arrangements wherein the modulating potentials are arranged to bring about opposite variations in both tuned circuits, it is not absolutely necessary for both said tuned circuits to be controlled since some results can be achieved by varying only one of the two tuned circuits. The described arrangement in which simultaneously opposite variation of both tuned circuits is obtained are, however, preferred. A

The present invention is of general application to the transmission of speech or music or to the transmission of telegraphic signals or facsmile signals or the like.

Having thus described my invention and the operation thereof, what I claim is:

1. In combination a source of constant frequency carrier frequency oscillations, a pair of energy transferring circuits, each including series inductances shunted by a tuning capacity,

a coupling between said source of carrier frequency oscillations and each of said energy transferring circuits, a load circuit coupled to receive energy from both of said energy transferring circuits, the sense of the various couplings being such that energy is transferred to the load cir'- cuit in a-differential manner, a pair of thermionic valves, each having its output circuit associated with a different one of the energy transferring circuits so as to control the natural frequency thereof, and means for applying modulating potentials to the input circuits of said modulating valves in phase opposition whereby opposite simultaneous control of said energy transferring circuits is obtained substantially as described.

2. ApparatusV as recited in claim l in which each modulating valve has in its plate circuit an inductance which is coupled to an inductance in a different one of the energy transferring cir- 20 cuits.

3. An arrangement as recited in claim l in which the two energy transferring circuits have portions in common.

4. A device as recited in claim l in which the source of oscillations is piezo-electrically or equivalently controlled as to frequency to secure constancy of frequency substantially as described.

5. An oscillation generator comprising, a thermionic tube having its electrodes connected in 'f Yoscillation producing circuits including an in- 5 ductance, a piezo-electric crystal in one of said circuits to insure the production of oscillations of constant frequency therein, a combined circuit comprising pairs of inductances connected in series, capacities in series shunting said pairs of inductances, an inductance connecting a point between said pairs of inductances to a point between said capacities said last named inductance being coupled to one of said rst named circuits, a load circuit including a pair of inductances each of said load inductances being coupled to an inductance of each of said first named pairs of inductances, a source of modulating potentials, a pair of thermionic tubes each having control grid, cathode and anode, a circuit connecting said control grids in phase opposition to said source of modulating potentials, an inductance connected between the anode and cathode of one of said tubes, said inductance being coupled to one of the inductances of one of said pairs of inductances, and an inductance connected between the anode and cathode of the other of said tubes, said inductance being coupled to one of the inductances of the other of said pair of inductances.

WILLIAM THEODORE DITCHAM. 

